The invention relates to a circuit arrangement for high-frequency operation of a discharge lamp, comprising input terminals for connection to a low-frequency supply voltage source, first rectifying means for generating a DC voltage across first capacitive means from a low-frequency supply voltage delivered by the low-frequency supply voltage source, a DC/AC converter for generating a high-frequency AC voltage with a frequency f from the DC voltage, a load branch comprising a series arrangement of inductive means, second capacitive means, and coupling means for coupling the discharge lamp to the load branch, which series arrangement connects a junction point N1 of the DC/AC converter to a junction point N2 between the first rectifying means and the first capacitive means, second rectifying means for converting a high-frequency voltage generated by means of the DC/AC converter into a DC voltage. The second rectifying means are coupled to the first capacitive means and to a junction point N3 in the load branch. Control means control the power consumed by the discharge lamp in dependence on a control signal which is a measure of the desired power.
Such a circuit arrangement is known from WO 96/10897. The first rectifying means in the known circuit arrangement are constructed as a voltage doubler, and the first capacitive means across which the voltage doubler generates a DC voltage comprise a first and a second capacitive impedance. The voltage across the first capacitive means is also referred to as a buffer voltage hereinafter. The load branch also comprises further capacitive means besides the inductive means, the second capacitive means, and the coupling means. A side of the further capacitive means is connected to the junction point N2. A further side of the further capacitive means is connected to the junction point N3. The power consumed by the discharge lamp, also referred to as lamp power hereinafter, can be controlled by control means which influence the frequency of switching elements of the DC/AC converter.
The first rectifying means are provided with first and second unidirectional means which at the same time form a part of second rectifying means. The second rectifying means are to ensure that the circuit arrangement substantially acts as a resistive impedance during lamp operation. In that case the circuit arrangement will cause little interference, and the circuit arrangement will have a high power factor during lamp operation. To achieve this, the buffer voltage must always be higher than a bottom value. If voltage doubling is used, this bottom value is equal to the peak-to-peak voltage of the low-frequency voltage source. The bottom value is equal to the peak-to-zero voltage if no voltage doubling takes place. The buffer voltage rises comparatively strongly in the known circuit arrangement in proportion as the power value is set lower. On the one hand, this requires a dimensioning of the circuit arrangement such that the buffer voltage is higher than the bottom value during nominal operation. On the other hand, components such as the switching elements and the first capacitive means must be designed for high voltages, or the range over which the lamp power is controllable must be limited so as to avoid damage to said components.